Production Characteristics and Properties of Cellulase/ Polygalacturonase by a Bacillus Coagulans Strain from a Fermenting Palm-Fruit Industrial Residue
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African Journal of Microbiology Research Vol. 3(8) pp. 407-417 August, 2009 Available online http://www.academicjournals.org/ajmr ISSN 1996-0808 ©2009 Academic Journals Full Length Research Paper Production characteristics and properties of cellulase/ polygalacturonase by a Bacillus coagulans strain from a fermenting palm-fruit industrial residue. 1* 1 2 O. A. Odeniyi , A. A. Onilude , and M. A. Ayodele 1Microbial Physiology and Biochemistry Research, Department of Botany and Microbiology, University of Ibadan, Ibadan, Nigeria. 2Germplasm Health Unit, International Institute of Tropical Agriculture, Ibadan, Nigeria. Accepted 9 July, 2009 A Bacillus coagulans strain isolated from palm fruit husk was tested for abilities to hydrolyse plant structural polysaccharides through the depolymerising activities of carboxymethylcellulase and polygalacturonase. The two enzymes were produced using solid substrate fermentation. Both had a working pH range of 4-9 with an optimum pH of 6.0 for the carboxymethylcellulase and 7.0 for the polygalacturonase. The respective enzymes remained active when allowed to stand at 27°C for 1 h over a wide pH and temperature range maintaining maximum activity at an optimum temperature of between 50°C and 60°C respectively. The Carboxymethylcellulase still retained full activity after being allowed to stand at 60°C for 10 min while the polygalacturonase retained full activity at 80°C for 5 min and had 50% activity at 70°C at 30 min. All enzymatic activities were fully inhibited by Mercury ions at 1.0 mM concentration. The carboxymethylcellulase had a molecular weight of between 116 and 205 KDa and another at 6.5 KDa. The molecular weight recorded for the polygalacturonase was 6.5 KDa. Polygalacturonase activity was enhanced by all surfactants applied while that of the cellulase was slightly enhanced by SDS and more by higher concentrations (0.5-5.0%) Tween-80. Key words: Physiological study, Bacillus coagulans, Carboxymethylcellulase, Polygalacturonase, Palm fruit husks. INTRODUCTION Plant structural polysaccharides, made up of complex, make up the cell wall. The microfibrils, crystalline and strongly bound micro fibrils of crystalline cellulose, paracrystaline core is surrounded by hemicellulose. After paracrystaline cellulose and hemicellulose fibrils, abound cellulose, this is the second most abundant plant polysac- in nature (Davidson et al., 2004; Pordesimo et al., 2005). charide in nature which serves as a storage component Cellulose, an important plant polymer has been found to in some seeds. Hemicellulose is a branched polymer structurally exist in crystalline molecules containing containing a mixture of hexoses (glucose, galactoman- thousands of glucose residues (Rose and Bennett, 1999). nans) and pentoses (xylose, arabinose) which cross-link Repeating units of cellulose is known to form a rigid with other individual microfibrils and structural polysac- structure due to close packing and the hydrogen bonding charides. in the cellulose sheets producing cellulose crystallites Microbial cultivation under solid state fermentation (Meyers, 1992; Li and Gao, 1997; Rose and Bennett, process is a procedure by which large biomass can be 1999). The association of the cellulose molecules with effectively harnessed to yield other advantageous by- the paracrystaline cellulose and other polymers result in products (Crueger and Crueger, 1997). The hydrolysis of the formation of microfibrils which, when tightly layered, plant components pose a big problem because of the complex bonding within the structural matrix as earlier defined. However, many plant pathogenic and non-plant pathogenic microorganisms produce cellulose and hemi- *Corresponding author. E-mail: [email protected]. cellulose-degrading enzymes which assist in plant cell 408 Afr. J. Microbiol. Res. colonization, invasion and degradation. Cellulases hydro- lution to detect clearing zones against a dark-brown background lyse both crystalline and paracrystaline cellulose structures (Fernandes-Salomao et al., 1996). while polygalacturonases cleave the -1,4-gly-cosidic bonds between two galacturonic residues (Alani et al., 2005; Ajayi Physiological responses of Bacillus strain to changes in et al., 2007). Residues from industrial agricultural practices environmental conditions abound throughout the different seasons experienced in the Tropics. In Nigeria, many such residues are conti- A culture broth of the Bacillus isolate was serially diluted out 6 nually generated but not adequately disposed of thus (Harrigan and MacCance, 1966) up to a colony count of 10 , generating environmental pollution problems. inoculated into sterile nutrient broth and incubated at varied tem- perature range between 27°C and 55°C. For the estimation of Nigeria is one of the leading producers of palm-oil and bacterial responses to pH variations, the pH of the broth medium the palm-fruit residues generated have been mainly was adjusted using 0.1 M citrate phosphate buffer to ranges of 4.0 enlisted to augment the strength of wood-fire, dumped as and 9.0, inoculated with the Bacillus and incubated at 37°C. The refuse or used as manure/or in composting (Oyenuga, effects of metal ion additions as either inhibitors or promoters were 1968). The ability of a microorganism to contribute in a monitored by adding 1.0 mM of any of the metal salts to the culture more effective degradation of palm-fruit husks through the broth and incubated for 4 days. In all cases, the absorbance of the test broth, as index of microbial growth, was measured at 600 nm array of enzymes produced is described in this work. This using a spectrophotometer, (Beckman DU 520, Beckman present investigation reports the production charac- Instruments, Fullerton CA, USA). terristics and properties of the hydrolytic cellulase and polygalacturonase of Bacillus coagulans from palm-fruit husk. Production of cellulases and polygalacturonases in Submerged Fermentation and Solid-State (SSF) The polygalacturonase-producing submerged fermentation medium MATERIALS AND METHODS of Marcia et al. (1999), with and without mechanical agitation, was used. The liquid medium containing (w/v) concentrations of 0.14% Materials (NH4)2SO4, 0.6% K2HPO4, 0.20% KH2PO4, 1.0% polygalacturonic acid and 0.01% MgSO4.7H2O at pH 6.0 was inoculated in 125 ml All reagents used were by Sigma-Aldrich, St Louis, Missouri, USA. Erlenmeyer flasks and incubated at 37°C on a rotary Orbit shaker bath, (Lab-line instruments, Illinois, USA) at 150 rpm for 60 h. Bacterial cellulase was produced using submerged fermentation in Sample collection flasks containing 25 ml of medium according to the method of Li and Gao (1997), with the following composition (%, w/v): 0.02 The fibrous palm-fruit husk residue, a by-product of palm-oil MgSO .7H O; 0.075 KNO ; 0.05 K HPO ; 0.002 FeSO .7H O; extraction process, was obtained from its dump site at Bodija in 4 2 3 2 4 4 2 0.004 CaCl2.2H2O; 0.2 Peptone with agar 1.5; and 0.5 Cellulose Ibadan Metropolis in the South-western region of Nigeria. This was was used with and without mechanical agitation. These were used as substrate for microbial isolation, cultivation and enzyme inoculated with a 106 cfu/ml of the Bacillus strain, incubated with production. agitation (150 rpm) at 37°C for 60 h, after which the biomass was separated by centrifugation at 10,000 rpm. The SSF was carried out in 250 ml Erlenmeyer flask containing 5 Isolation and culture methods g of palm-fruit husk wetted with 10 ml of a basal mineral salt medium with the following composition: 1% (NH4)2SO4; 0.06% The Bacillus strain was isolated from fermenting palm-fruit husk by K2HPO4; 0.05% KH2PO4; 0.04 mg CuSO4.5H2O and 0.02% direct plating of ten-fold serial dilutions of samples (Harrigan and MgSO4.7H2O. The set-up was steam-sterilized at 121°C, inoculated MacCance, 1966). Isolate selection was a consequence of the with a 106 cfu/ml culture and incubated at 37°C for 96 h. After production of large, clear zones on both cellulose and polygala- inoculation, the fermented material was mixed with eight volumes cturonic acid agar plates. The bacterium was identified according to its size of sterile distilled water, mechanically agitated at 150 rpm standard cultural, biochemical and physical characteristics. Experi- for 30 min and filtered under vacuum to separate the solid-liquid mental isolate was maintained on a nutritive and supportive agar phase. The cell-free enzyme filtrate was harvested after cold- medium containing 0.1% carboxymethyl cellulose or 0.1% Polyg- centrifugation (4°C) at 10,000 rpm for 15 min and used to evaluate alacturonic acid, and stored at 4°C in a cold room. the cellulose and polygalacturonic acid-degrading enzymatic activities. The effect of incubation time; pH and medium agitation were Screening for enzymes production tested to determine optimized cellulase and polygalacturonase production. The enzymatic culture medium was prepared in 0.1 M Cellulose agar plates were prepared using the method of Andro et citrate-phosphate buffer within ranges of 4.0 and 9.0. Cultivation al. (1984). The Bacillus isolate was stabbed on the solidified agar was in 125 ml Erlenmeyer flasks with 25 ml of medium and the and allowed to incubate for 2 days to express cellulose depolyme- submerged fermentation culture mechanically agitated on a rotary risation through cellulase production into its surrounding medium. shaker at 150 rpm. Samples were withdrawn at 24 h intervals and The plate was stained with 0.1% Congo red (pH 7.0) and used to determine the extent of enzyme production. counterstained with 1.0 M NaCl for 15-20 min. The zone of polymer hydrolysis was apparent as a clear area in the otherwise red CMC Congo red stained background. Polygalacturonase production was Enzyme assays screened for by the method of Marcia et al. (1999). The agar plate containing this medium was stabbed with the isolate and incubated Carboxymethylcellulase: The modified method of Robson and for 2 days. The plate was flooded with Iodine-Potassium iodide so- Chambliss (1984) was used.